Differences between the number of system users, concurrent users, and online users and Calculation

Assume that there is an OA system with 2000 users-that is to say, the total number of users who may use the OA system is 2000. This concept is "number of system users ", the system has an "online statistics" function (the system uses a global variable to count all logged-on users), which can be obtained from the online statistics function, at the peak, 500 people are online (this 500 is generally referred to as "concurrent online users"). What are the number of concurrent users of the system?
According to our definition of the number of concurrent users of the business, this 500 represents the maximum number of concurrent users of the business in the system. Of course, the value 500 only indicates that 500 users have logged on to the system at the peak, not the pressure on the actual server. Because the pressure on the server is also related to the specific user access mode. For example, in these 500 "using the system at the same time" users, we can examine a certain time point, assume that 40% of users are interested in viewing system announcements (Note: The "View" action does not impose any burden on the server ), 20% of Users fill in complex forms (for the forms entered by users, requests are sent to the server only when they are "submitted", and the filling process does not put pressure on the server ), 20% of users are in a daze (that is, nothing is done), and the remaining 20% users are constantly switching from one page to another. In this scenario, we can say that, only 20% of users really put pressure on the server. Therefore, from the above example, we can see that the actual pressure on the server depends not only on the number of concurrent users of the business, but also on the user's business scenario.
In the actual performance testing work, the tester is generally concerned with the number of concurrent users of the business, that is, from the business perspective, it is reasonable to pay attention to the number of concurrency settings. Therefore, in the subsequent discussions, we will also discuss the number of concurrent users of the business. In addition, for convenience, the number of concurrent users of the business is called the number of concurrent users.
(1) calculate the average number of concurrent users: c = NL/T
(2) peak number of concurrent users: c '≈ C + 3 C
In formula (1), C indicates the average number of concurrent users, N indicates the number of login sessions, L indicates the average length of login sessions, and t indicates the length of the tested time period.
Formula (2) calculates the peak number of concurrent users. Among them, C' refers to the peak number of concurrent users, and C refers to the average number of concurrent users obtained in formula (1. This formula is obtained by assuming that the login session generated by the user conforms to the Poisson distribution.
Instance:
Assume that there is an OA system with 3000 users. On average, about 400 users access the system every day. For a typical user, the average time a user logs on to the system within one day is 4 hours. Within one day, the user only uses the system within 8 hours.
Then, according to the formula (1) and formula (2), we can get:
C = 400*4/8 = 200
C '≈ 200 + 3 * root code 200 = 242